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arXiv 0804.1520astro-ph
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汉堡/ESO巡天的恒星内容。IV。候选贫金属星的选择

The stellar content of the Hamburg/ESO survey. IV. Selection of candidate metal-poor stars

N. Christlieb, T. Schoerck, A. Frebel, T. C. Beers, L. Wisotzki, D. Reimers

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11 pages, 10 figures, accepted for publication in A&A
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摘要：

本文介绍了在汉堡/ESO物棱镜巡天（HES）中选择贫金属星的定量方法。选择是基于Ca II K线的强度，B-V颜色（两者都直接从数字HES光谱测量），以及来自2微米全天巡天的J-K颜色。Ca II K的KP指数可以从HES光谱中测量，精度为1.0埃，并且使用CCD测光对HES B-V颜色进行校准，对于颜色范围为0.3 < B-V < 1.4的恒星，产生0.07 mag的1-sigma不确定度。这些精确度使得有可能可靠地拒绝[Fe/H] > -2.0的恒星，而不会牺牲最低金属丰度的完整性。使用存在于HES板上的1121颗来自香港Beers、Preston和Shectman巡天的恒星进行的选择测试表明，在[Fe/H] < -3.5处的完整性接近100%，同时，候选样品的假阳性污染很低：50%的[Fe/H] > -2.5的恒星和97%的[Fe/H] > -2.0的恒星被拒绝。这个选择被应用到379个HES场，覆盖了南银河高纬度天空的8853平方度的名义面积。候选样本由20，271颗星等范围为10 < B < 18的恒星组成。与香港巡天的星等分布比较表明，HES样本的星等极限比香港巡天的星等极限要暗2等。考虑到两次巡天覆盖的天空区域重叠，因此，相对于香港巡天，太阳能卫星对贫金属星的巡天量增加了约10倍。我们已经用HES鉴定了几个非常罕见的物体，包括，例如，是目前已知的三颗最缺乏重元素的恒星。

英文摘要：

We present the quantitative methods used for selecting candidate metal-poor stars in the Hamburg/ESO objective-prism survey (HES). The selection is based on the strength of the Ca II K line, B-V colors (both measured directly from the digital HES spectra), as well as J-K colors from the 2 Micron All Sky Survey. The KP index for Ca II K can be measured from the HES spectra with an accuracy of 1.0 Angstrom, and a calibration of the HES B-V colors, using CCD photometry, yields a 1-sigma uncertainty of 0.07 mag for stars in the color range 0.3 < B-V < 1.4. These accuracies make it possible to reliably reject stars with [Fe/H] > -2.0 without sacrificing completeness at the lowest metallicities. A test of the selection using 1121 stars of the HK survey of Beers, Preston, and Shectman present on HES plates suggests that the completeness at [Fe/H] < -3.5 is close to 100% and that, at the same time, the contamination of the candidate sample with false positives is low: 50% of all stars with [Fe/H] > -2.5 and 97% of all stars with [Fe/H] > -2.0 are rejected. The selection was applied to 379 HES fields, covering a nominal area of 8853 square degrees of the southern high Galactic latitude sky. The candidate sample consists of 20,271 stars in the magnitude range 10 < B < 18. A comparison of the magnitude distribution with that of the HK survey shows that the magnitude limit of the HES sample is about 2 mag fainter. Taking the overlap of the sky areas covered by both surveys into account, it follows that the survey volume for metal-poor stars has been increased by the HES by about a factor of 10 with respect to the HK survey. We have already identified several very rare objects with the HES, including, e.g., the three most heavy-element deficient stars currently known.

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